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1 /*
2  * Copyright (C) 2017 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef NETD_SERVER_NETLINK_UTIL_H
18 #define NETD_SERVER_NETLINK_UTIL_H
19 
20 #include <functional>
21 #include <linux/netlink.h>
22 #include <linux/rtnetlink.h>
23 
24 #include "NetdConstants.h"
25 
26 namespace android {
27 namespace net {
28 
29 const sockaddr_nl KERNEL_NLADDR = {AF_NETLINK, 0, 0, 0};
30 
31 const uint16_t NETLINK_REQUEST_FLAGS = NLM_F_REQUEST | NLM_F_ACK;
32 const uint16_t NETLINK_ROUTE_CREATE_FLAGS = NETLINK_REQUEST_FLAGS | NLM_F_CREATE | NLM_F_EXCL;
33 // Don't create rules with NLM_F_EXCL, because operations such as changing network permissions rely
34 // on make-before-break. The kernel did not complain about duplicate rules until ~4.9, at which
35 // point it started returning EEXIST. See for example b/69607866 . We can't just ignore the EEXIST
36 // because if we hit it, the rule was not created, but we will think it was, and we'll then trip up
37 // trying to delete it.
38 const uint16_t NETLINK_RULE_CREATE_FLAGS = NETLINK_REQUEST_FLAGS | NLM_F_CREATE;
39 const uint16_t NETLINK_DUMP_FLAGS = NLM_F_REQUEST | NLM_F_DUMP;
40 
41 // Generic code for processing netlink dumps.
42 const int kNetlinkDumpBufferSize = 8192;
43 typedef std::function<void(nlmsghdr *)> NetlinkDumpCallback;
44 typedef std::function<bool(nlmsghdr *)> NetlinkDumpFilter;
45 
46 // Opens an RTNetlink socket and connects it to the kernel.
47 WARN_UNUSED_RESULT int openNetlinkSocket(int protocol);
48 
49 // Receives a netlink ACK. Returns 0 if the command succeeded or negative errno if the command
50 // failed or receiving the ACK failed.
51 WARN_UNUSED_RESULT int recvNetlinkAck(int sock);
52 
53 // Sends a netlink request and possibly expects an ACK. The first element of iov should be null and
54 // will be set to the netlink message headerheader. The subsequent elements are the contents of the
55 // request.
56 
57 // Disable optimizations in ASan build.
58 // ASan reports an out-of-bounds 32-bit(!) access in the first loop of the
59 // function (over iov[]).
60 #ifdef __clang__
61 #if __has_feature(address_sanitizer)
62 __attribute__((optnone))
63 #endif
64 #endif
65 WARN_UNUSED_RESULT int sendNetlinkRequest(uint16_t action, uint16_t flags, iovec* iov, int iovlen,
66                                           const NetlinkDumpCallback *callback);
67 
68 // Processes a netlink dump, passing every message to the specified |callback|.
69 WARN_UNUSED_RESULT int processNetlinkDump(int sock, const NetlinkDumpCallback& callback);
70 
71 // Flushes netlink objects that take an rtmsg structure (FIB rules, routes...). |getAction| and
72 // |deleteAction| specify the netlink message types, e.g., RTM_GETRULE and RTM_DELRULE.
73 // |shouldDelete| specifies whether a given object should be deleted or not. |what| is a
74 // human-readable name for the objects being flushed, e.g. "rules".
75 WARN_UNUSED_RESULT int rtNetlinkFlush(uint16_t getAction, uint16_t deleteAction,
76                                       const char *what, const NetlinkDumpFilter& shouldDelete);
77 
78 // Returns the value of the specific __u32 attribute, or 0 if the attribute was not present.
79 uint32_t getRtmU32Attribute(const nlmsghdr *nlh, int attribute);
80 
81 }  // namespace net
82 }  // namespace android
83 
84 #endif  // NETD_SERVER_NETLINK_UTIL_H
85